Childhood obesity affects approximately 7% of the Chilean population less than 6 years old. Inspite of multiple efforts in the treatment of obesity the results continue to be poor. One factor that may influence these results is an erroneous parental perception of the nutritional status of their obese children. Using a questionnaire we interviewed 64 mothers of obese children who regularly attend the Penco Lirquen Hospital. We found a high level of awareness of understanding that obesity is a pathological condition (98.4%). However the mothers had an altered perception of the nutritional status of their children. 37.5% thought their children were only slightly obese and 26.6% as having a normal weight. This could partly explain the elevated percentage of failures in the treatment of childhood obesity. We recommend that in future treatment strategies of obese children that the parental perception of the nutritional state should be previously defined